In
the spring of 1915, the Allies undertook naval and land operations
in the Dardanelles that were intended to knock the Ottoman Empire
out of the war with one blow and to open the straits for the passage
of supplies to Russia. Amphibious landings were carried out at Gallipoli,
but British forces, vigorously opposed by forces commanded by Atatürk,
were unable to expand their beachheads. The last units of the expeditionary
force were evacuated by February 1916.

In Mesopotamia the Ottoman army defeated a British
expeditionary force that had marched on Baghdad from a base established
at Basra in 1915. The British mounted a new offensive in 1917, taking
Baghdad and driving Ottoman forces out of Mesopotamia. In eastern
Anatolia, Russian armies won a series of battles that carried their
control west to Erzincan by July 1916, although Atatürk, who
was then given command of the eastern front, led a counteroffensive
that checked the Russian advance. Russia left the war after the
Bolshevik Revolution in 1917. The new Russian government concluded
the Treaty of Brest-Litovsk with the Central Powers in March 1918,
under which the Ottoman Empire regained its eastern provinces.

Sharif Husayn ibn Ali, the sultan's regent in
Mecca and the Hijaz region of western Arabia, launched the Arab
Revolt in 1916. The British provided advisers, of whom T.E. Lawrence
was to become the best known, as well as supplies. In October 1917,
British forces in Egypt opened an offensive into Palestine; they
took Jerusalem by December. After hard fighting, British and Arab
forces entered Damascus in October 1918. Late in the campaign, Atatürk
succeeded to command of Turkish forces in Syria and withdrew many
units intact into Anatolia.